With the development of economy and the progress of science and technology, the advanced technology about electrical appliance in the field of high and new technology emerges in endlessly, and the electrical appliance industry becomes one of the most rapid development industries in 20th century. Because of the use of electronic products and the progress of related technology, the abandonment and update cycle time of electronic products continuously shortened, and the number of electronic waste was growing day by day. The United States produces the largest number of electronic products and electronic junk in the world, while the production of electronic waste is as high as 700 to 800 million tons every year, and the number is becoming more and more larger. The amount of electronic waste of the whole Europe is about 6 million tons every year, Germany is 1.8 million tons, and France is 1.5 million tons. Since 2007, China had reached the home appliance update peak. It is about 5 million TV sets, 4 million refrigerators, 6 million washing machines, 10 million computers and tens of millions of mobile phones scraped every year. The United Nations Environment Programme (UNEP) issued a report called “the electronic waste recycling-for resources”, which showed that waste computers, printers, mobile phones, audio-visual equipments, refrigerators, toys and TV sets and other electronic junk are growing by 40 million tons per year. The situation in the developing countries, where the economic growth speed is faster and faster, is especially worrying. “By the year 2020, the number of waste computers will be double or more than two times of 2007 in South Africa and China, and 5 times in India. By then, the number of abandoned mobile phones in China will grow to 7 times, and which will increases 18 times in India. Besides the number of abandoned televisions will increased by 1.5 to 2 times in China and India, the number of abandoned fridges will grow by 2 to 3 times in India”. Electronic waste is becoming a new hazardous waste pollution source.
WPCB are the part, which is the most difficult to deal with, and has the heaviest burden to the environment, and has also the highest added value in Electronic waste. Printed circuit boards are made of the resin and a variety of metal mixes. If they are not properly treated, the brominated flame retardants carcinogen and heavy metal, which are contained in the printed circuit boards, will do a great harm to soil and human health. But the WPCB contain a variety of valuable metals (such as Cu, Pb and Sn) and precious metals (such as Au, Ag, Pt and Pd). The content of these metals in WPCB is a few times higher or tens of times higher than the ordinary mineral. So the recycling of the valuable metals in WPCB can bring high economic value.
Pyrometallurgical process was used to get metallurgy metal from WPCB in traditional methods. The WPCB were burned to remove the substrate organic materials, and then the simple metal substance was formed from the rest metals by smelting and electrolytic reaction. There were organic produced a lot of poisonous and harmful gas by organic matter burned, what can cause serious pollution on the environment by only a little emissions. It was difficult to treat with the waste gas, and the equipment investment is large. In order to avoid pollution, there were several physical methods about the recycling process of the WPCB proposed one after another at home and abroad. For example, U.S. Pat. No. 5,683,040 putted forward a kind of mechanical and physical method, in which the electronic devices of the circuit boards were taken apart and the undamaged electronic devices were recycled. After the circuit boards crushed and grinded, and the metallic and nonmetallic were separated through the sorting equipments. During China's patent 99102862.7, 02121434.4, 03113180.8 and 200310103403, WPCB were separated to the metallic and nonmetallic by the methods of mechanical broken and magnetic separation. With these methods, the costs of equipments production were high, and ultimately the metallic and nonmetallic powders were obtained. The metal simple substance cannot be obtained completely, so that it had a low added value. It was reported in China's patent 98105592.3 that there was a kind of metal crushing reaction method for metal simple substance recycling. But the process was complex, the recovery efficiency was low, the production equipment investment cost was high and energy consumption was huge. A method about the recovery of copper and aluminum metal from WPCB was mentioned in Japan's patent JP2005000841 and China's patent 200610117802.6. But the method was complex, the recovery efficiency was low, and it was only for a certain metal recycling, so that it can't achieve the goal of valuable metals' comprehensive recycling from WPCB. In China's patent 200710176776.9, it was referred to a kind of method about classification electrolysis for the metal recovery in electronic waste. It can recover the Cu, Zn, Pb, Ag, Pt and Au in WPCB by fractional electrolysis. But the aqua regia and other acid were used in this method, which can strength the environmental burden. And all the metals were recycled by the electrolysis process, which had high energy consumption and large recovery cost.